STANDBY and RTC

[sami]

Posted on April 15, 2013 at 15:14

Hi Again ;

In my application stm32f407 will enter stanfby mode then should wake up by 2 methods ; a rising edge on the PA0( wakeup _pin) and an alarm occurs everyday one time .. the first one I thing I will not get problem the sec?nd one confused me after we have finished the PCB, is it possible to wakeup from standby using RTC alarm without external wirring ? #lse-rtc

[Tesla DeLorean]

Posted on April 15, 2013 at 16:49

RTC Alarm wake from standby requires no PCB magic. You will however require a supply on VBAT and an LSE crystal.

[sami]

Posted on April 15, 2013 at 18:36

Thank you Clive ;

I could do it , but now I have 5mA standby current !! what could be the problem?

[Tesla DeLorean]

Posted on April 15, 2013 at 18:42

On what supply?

Consider what you have attached to the chip, and the state of the GPIO pins, and the circuits/nets to which they are attached. Do you happen to have anything going on with PC13, PC14, PC15 and PI8? Is PDR_ON pulled high? or floating?

[sami]

Posted on April 15, 2013 at 18:49 PC13, PC14, PC15  are floating . PDR_ON pulled low because I am using F407 100 pins ( PDR_on shown as vss ),is that ok? On the other GPIO I have some pull ups and pull downs and some usart and ADC but as I know is standby mode they are high impedence. Thank you clive

[Tesla DeLorean]

Posted on April 15, 2013 at 18:56

The pins I mentioned are in the BKP/PWR domain, at least two should be connected to LSE. Anything connected to them with draw from VBAT.

Others have reported high current issues on VBAT.

https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Vdd%20being%20held%20at%7V%20with%20backup%20battery%20fitted&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06...

[DEAD LINK /public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Vbat%20problem%20on%20a%20STM32F4&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&currentviews=473]https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=%2Fpublic%2FSTe2ecommunities%2Fmcu%2FLists%2Fcortex_mx_stm32%2FVbat%20problem%20on%20a%20STM32F4&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B¤tviews=473 Where are you measuring the current? On what supply?

[sami]

Posted on April 15, 2013 at 19:09 My design operates  from VBAT , so I am measuring the current drawn from VBAT directly ; while operating in normal mode it draws 45mA I expect this so ok  , but in standby mode I expect some uAs  only but its 4,5mA -5mA ..!! The guys mentioned about PDR_ON  that should pulled up but in my device its shown as vss ! is that ok ?

[Tesla DeLorean]

Posted on April 15, 2013 at 19:17

Hard to say, I don't have an F2/F4 strapped up in a suitable configuration.

When I did some aggressive testing on an F1 design. STOP pulled about 1mA, and STANDBY 180uA at my 3.7V lithium cell.

[jpeacock2399]

Posted on April 16, 2013 at 16:05

PC14, PC15 are floating .

This means you don't have an external oscillator or crystal connected to the RTC LSE.  Without an LSE you can't use the RTC when it's powered down, because there's no clock to drive the RTC.  Your alarm will never trigger because the RTC doesn't increment.

  Jack Peacock

[sami]

Posted on April 16, 2013 at 21:41 Sorry Jack  those pins are not floaing I have LSE there . Now I have about 100uA standby current I changed the pullup resistors in my circuit that  strange ..because in standby mode the GPIO should be high impedence. even 100uA is still high because the datasheet as I remmember in the datasheet its about 35uA. Thank you Clive and JAck